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paste quality

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paste quality | 10 February, 2014


I wanted to know how can we test our paste quality, as viscosity, temperature in which it is delivered to the SMT line and other variables that can affect our paste dispense or soldering. Our concerns are that paste quality may be causing solder balls on the component pads, or may be you can give us an probable cause to this and how can I avoid on my product.


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paste quality | 10 February, 2014

It is sort of a self answering question if you come in from the solder paste angle.

First....start gathering data. Check every day, or every new paste jar, for: Storage conditions (temp), paste expiration date, ambient temp and humidity where you are using the paste, warm up time, and a viscosity check. Maybe even some test print data. (SPI)

You might be able to start correlating the data against your soldering defects. Over time you may notice trends, for example, whenever it is warmer and more humid than normal, you might start to see more solder balling on the board. Things similar to that. The assumption here, of course, is that the paste is the issue for your defects.

From the other side, you might look at the defects from a process viewpoint. Solder balls are caused by X, or Y, or Z in your process. Eliminate those major things right up front.

In short, if you are taking good care of your solder paste, it should take pretty good care of you. If you don't take care of your paste, you could be chasing defects, (and collecting data)from here till sundown.

Hope that is of some help 'hege

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paste quality | 11 February, 2014

You should get your paste in ice(dry ice). Then you should keep it in a fridge. Many pastes now have 1month shelf life(after you take it out of the fridge). If you follow all the above, you might be having:

1. Lot problem - try different lots of your paste to prove it 2. Have a process issue - not connected with the paste

I would also try different paste manufacturer to prove the quality of your paste - buy one jar from different manufacturer and observe results.

Regards, Emil

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paste quality | 11 February, 2014

Perhaps a photo of the faults you are encountering might shed some light on the issue. I would think it would take some extremely poor paste handling or paste for the paste itself to be the root cause of what you seem to be describing. I would be inclined to be check all my other process parameters, reflow profiles, stencil apertures and PCB pad sizes.

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paste quality | 11 February, 2014

Jigo, We have never had a need to do internal testing on solder paste, and your paste supplier should be able to tell you what the correct operating temperature range is. All of the big names in solder paste have tight quality control and I suspect they all produce a good product these days.

If you think you are having a problem with your paste quality, I would have your paste manufacturer send in a technical guy. If they are a good company they will do this free of charge.

The first thing they will most likely want to look at is your reflow profile.

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paste quality | 13 February, 2014

Have to agree with Sr Tech and Spoilt - you'd have to really mistreat your paste these days for it to be the root cause. However, try another paste to eliminate that; making sure you abide by the suppliers specs.

Pad design, stencil design,(including thickness), reflow profile are the first areas to look at. If everything else is OK it's probably not the profile. Component termination material may be a cause. We also suspect solder mask contamination causing inferior wetting sometimes. We have an 1812 ferrite inductor that I home plate on the stencil for one assembly. We use this inductor on nearly every job we do, but this is the only one that causes trouble. There's a large copper plane underneath the area which may have something to do with it.

Compare the product with another similar one where you don't have problems with if you can. But I guess you've done that...

Get your paste supplier in to give you a hand.

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